textproduct: Rapid City

KEY MESSAGES

- Widespread rainfall still looks likely overnight.

- Becoming windy on Monday, especially across the northwest.

- Fire weather concerns on Monday are the wildcard on Monday across the northwest.

DISCUSSION

(This Evening Through Sunday) Issued at 1232 PM MDT Sun Sep 13 2026

Latest water vapor imagery shows 500hpa low spinning across southern WA state with ridging setting up from eastern MT into eastern CO. Upper flow across the Dakotas has turned more northwesterly with broad cyclonic flow setting up across the Great Lakes into New England. Broad high pressure still remains in control across the southern tier of states. At the surface, low pressure is setting up across southern WY. Southeast surface winds ahead of this low are advecting in a lower cloud deck out of NE into much of the forecast area. Temperatures at 18Z are in the low to mid 60s.

The forecast through the next 24 hours presents some interesting challenges. First in a series of shortwaves ejects into the FA this evening, with strengthening 700hpa theta-e forcing and moisture advection, as seen with increasing 850hpa dewpoints. This should lead to increasing coverage of rainfall across the forecast area beginning later this evening and continuing through the night. Cant rule out some elevated convection. Hi-res models are showing the potential for some of these storms to mix down the strong 700hpa and 850hpa winds as well. The rain will be welcome for sure. On Monday, the rain will push east of the FA during the morning hours. The cold front sweeps through with gusty NW winds found on the backside along with modest CAA. By 18Z Monday models are showing from 4 to 5 mb/3hrly pressure rises on backside of front. It appears that winds will become nearly linked during the afternoon hours, so have opted to hoist a wind advisory for parts of our northern FA during the day Monday. This also leads to a tricky fire weather concern. Parts of our NW are at critical fire danger levels. The unknown is how much rain they may receive overnight, helping to put a small damper on those critical levels. Additionally, there might only be a narrow window when RH values and winds meet up for fire weather headlines. For now, am going to forego any fire weather headlines and let later shifts evaluate. Also, given CAA and anticipated cloud cover, lowered high temperatures on Monday.

After Monday, the rest of the week still appears to be seasonable temperature wise. Precipitation chances move back into the area beginning late Tuesday night and generally continue through the rest of the week.

AVIATION

(For the 18Z TAFS Through 18Z Monday) Issued At 1119 AM MDT Sun Sep 13 2026

This forecast period presents a more involved scenario. For this afternoon, conditions will remain gusty and VFR for the area. A deck of lower clouds has moved in to south-central SD, which looks to persist through the evening into tonight. MVFR/IFR cloud decks will impact western SD tonight, lasting into Monday morning well after sunrise. Also overnight, transient showers will impact western SD and northeastern WY. Stronger storm cores may be capable of MVFR/IFR conditions in the form of reduced visibilities and lower ceilings if they are not already present. Alongside possible TSRA, a front will move through, shifting winds to northwesterly. This will impact KGCC around 11Z and KRAP around 16Z.

UNR WATCHES/WARNINGS/ADVISORIES

SD...Wind Advisory from 11 AM to 9 PM MDT Monday for SDZ001-002- 012>014-073-078. WY...None.